1. Field of Invention
The present invention relates to access mounting flanges for tubing, containers or vessels used in chemical processing at relatively cold temperatures.
2. Description of Prior Art
It has been conventional practice in chemical processing to cover containers and pipe walls with coatings of foam or other insulative materials. Normally, these materials have been covered within protective jackets or covers. For reasons of safety and also environmental protection, it has been required to periodically inspect or monitor the walls of these containers or pipes. For this reason, access ports or holes have been drilled or otherwise formed in the insulation to provide access through the insulation to the wall.
U.S. Pat. No. 5,351,718, of which applicant is inventor, relates to an access plug flange assembly which is adapted to be fitted into insulative coverings for chemical processing equipment. Structure according to applicant's prior U.S. Patent has proven useful in a wide variety of situations with chemical processing equipment insulative coverings. However, where the processing involved relatively cold applications (typically -40.degree. F. or lower) several additional problems have still existed.
The normal protective vapor barrier coating around the insulation on the metal tube or vessel wall had to be removed at the test location, leaving an air path through the vapor barrier. Ambient air entering these access plug flanges was generally considerably warmer than the processing temperatures of the cold processing equipment. It also contained moisture due to the general presence of atmospheric humidity. The moisture in the relatively warm ambient air generally froze on the cold metal equipment walls within prior access plug flanges on processing equipment. As a result, a plug or body of ice formed within the flange on the equipment wall. In order for accurate test readings to be obtained in the flange, the ice had to be removed so that the test probe actually contacted the equipment wall.
This usually required that the ice be chipped away, which was a time consuming process. Further, either the insulation or the equipment wall, or both, could be damaged during such chipping. If readings were made without removing the ice, they were erroneous and of no value. Also, in processing equipment which cycled above and below cold temperatures, the ice could melt and the resulting liquid within the flange could penetrate the insulative coating and damage it. The liquid which penetrated into the insulative coating could then refreeze, hampering the effectiveness of the insulation for its intended purpose. The liquid also could refreeze inside the flange, again forming an undesirable block or plug. Presence of the frozen liquid in the flange also made it difficult to remove an installed plug flange without damaging both the flange assembly and the insulative coating.